Synthesis, structures and ε-caprolactone polymerization activity of aluminum N,N′-dimethyloxalamidates

Alkyl aluminum N,N′-dimethyloxalamidates R₄Al₂(dmoa) (1, R = Me; 2, R = Et; 3, R = ⁱBu; 4, R = ^tBu) (dmoa-H₂ = N,N′-dimethyloxalamide) have been prepared and characterized. Molecular structures of the compounds 1 and 4 have been determined by X-ray crystallography. The centrosymmetric molecules of the compounds consist of one N,N′-dimethyloxalamidate unit bonded to two four-coordinated aluminum atoms. Each of the aluminum atoms is bonded to two alkyl groups, and oxygen and nitrogen atoms originating from two different amidate groups. A skeleton framework of the molecules of 1 and 4 consists of two fused AlNOC₂ heterocyclic rings, which are flat and positioned in one plane. It was shown that compounds 1-3 were initiators in a process of ring opening polymerization (ROP) of ε-caprolactone. The compound 4 exhibited low activity in ROP.     

Enantioselective Friedel-Crafts reaction of acylpyrroles with glyoxylates catalyzed by BINOL-Ti(IV) complexes

We report the first efficient enantioselective Friedel-Crafts hydroxyalkylation of pyrroles having one electron-withdrawing group at the α, β or N-positions with alkyl glyoxylates catalyzed by readily available chiral BINOL-Ti(IV) complexes (1-5 mol %). The reaction regioselectively led to the desired pyrrole-hydroxyacetic acid derivatives with good yields (70-96%) and enantiomeric excesses up to 96%, and is applicable in multigram scale with low loading of the catalyst (1 mol %).     

Charge transfer in porphyrin-calixarene complexes: ultrafast kinetics, cyclic voltammetry, and DFT calculations

Transient absorption spectroscopy, cyclic voltammetry, and DFT calculations were used to describe charge transfer processes in a series of 5,10,15,20-tetrakis(N-methylpyridinium-n-yl) porphyrins (TMPyPn, n = 4,3,2) and TMPyPn/p-sulfonatocalix[m]arene (clxm, m = 4,6,8) complexes. Excitation of TMPyPn is accompanied by an increasing electron density at the methylpyridinium substituents in the order TMPyP2 < TMPyP3 < TMPyP4. The quenching of the excited singlet states of the complexes increases with the number of ionized phenolic groups of clxm and can be correlated with the partial transfer of the electron density from O(-) to the peripheral methylpyridinium substituents rather than to the porphyrin ring.     

Thermal behavior and decomposition kinetics of Formex-bonded explosives containing different cyclic nitramines

Thermal behavior and decomposition kinetics of Formex-bonded PBXs based on some attractive cyclic nitramines, such as 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Actually, cis-1,3,4,6-tetranitrooctahy droimidazo-[4,5-d]imidazole (BCHMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10, 12-hexaazaisowurtzitane (CL-20), was investigated by means of nonisothermal thermogravimetry (TG) and differential scanning calorimetry (DSC). It was found that the mass loss rate of PBXs involved in this research depends greatly on heating rate and the residue of the decomposition of these PBXs decreases with the heating rate. The onset of the exotherms was noticed at 215.4, 278.7, 231.2 and 233.7 °C with the peak maximum at 235.1, 279.0, 231.2 and 233.7 °C for RDX-Formex, HMX-Formex, CL-20-Formex, and BCHMX-Formex, respectively. Their corresponding exothermic changes were 1788, 1237, 691, and 1583 J g^?1. It was also observed that the dependence on the heating rate for onset temperatures of HMX- and BCHMX-based PBXs was almost the same due to their similar molecular structure. In addition, based on nonisothermal TG data, the kinetic parameters for thermal decomposition of these PBXs were calculated by isoconversional methods. It was shown that the Formex base has great effects on the activation energy distribution of nitramines. It was further found that the kinetic compensation effects occurred during the thermal decomposition of nitramine-based PBXs, and they almost have the same compensation effects due to similar decomposition mechanism.     

3He NMR: from free gas to its encapsulation in fullerene

The ³He nuclear magnetic shieldings were calculated for single helium atom, its dimer, simple models of fullerene cages (He@C_n), and single wall carbon nanotubes. The performances of several levels of theory (HF, MP2, DFT‐VSXC, CCSD, CCSD(T), and CCSDT) were tested. Two sets of polarization‐consistent basis sets were used (pcS‐n and aug‐pcS‐n), and an estimate of ³He nuclear magnetic shieldings in the complete basis set limit using a two‐parameter fit was established. Theoretical ³He results reproduced accurately previously reported theoretical values for helium gas, dimer, and helium probe inside several fullerene cages. Excellent agreement with experimental values was achieved. ³He nuclear magnetic shieldings of single helium atom approaching various points of benzene ring were tested, and an impact of ³He confinement within fullerene cages of different size on the ³He chemical shift was determined. Copyright © 2013 John Wiley & Sons, Ltd.     

New SRDN-3 probes with a semi-conductor detector for measuring radon activity concentration in underground spaces

The article presents new Polish probes SRDN-3, developed at the Institute of Nuclear Chemistry and Technology in Warsaw, equipped with a semi-conductor detector used for continuous measurements of ²²²Rn activity concentration. Due to a relatively high lower detection limit, the device is dedicated for use in underground spaces—caves, adits, mines, tourist routes in strongholds, pyramids, etc. Its structure allows for difficult conditions in which the device is transported to the measurement site, as well as hard operating conditions caused chiefly by large ambient relative humidity, reaching up to 100%. The authors present calibration results of these appliances, as well as the results of their work in a cave and an adit in the Sudetes (SW Poland). After almost 2 years of working in difficult conditions, the probes displayed high reliability. No defects of the semi-conductor detectors or the electronics were observed, which ensured problem-free communication of the probe-programmer-PC set. Thanks to this, the authors have a 2 year stock of data, recorded hourly by five probes, at their disposal. The only element that did not withstand the test of extreme operating conditions was one of the combined relative humidity and temperature sensors. No powering problems were observed either, and the batteries were replaced once a year, before the winter season. Also the programmer functioned faultlessly, enabling data transmission to a PC, which, being much more sensitive to operating conditions, had been placed away from the site of probe exposure. After using more sensitive temperature, relative humidity and pressure sensors, SRDN-3 probes will certainly prove an excellent tool for microclimate measurements (including measurement of air-atmosphere exchange) in caves and other underground sites. Even nowadays they are already a satisfactory tool for monitoring ²²²Rn concentration in underground spaces.     

Preparation of inorganic crystalline compounds induced by ionizing,UV and laser radiations

Results on preparation of nickel, zinc, yttrium, aluminum and cobalt oxides, zinc peroxide and hydroxide, yttrium and lutetium aluminum garnets and cobalt(II) aluminate via irradiation of aqueous solutions containing soluble metal salts and radical scavengers (formate anion or propan-2-ol) are summarized in this paper. Various physico-chemical and structural properties of prepared compounds (e.g. crystallinity, specific surface area, particle size) are also reported.All used variants of radiation method are rather convenient and simple, and yield nano-scale powder materials with interesting characteristics. Prepared materials generally have high chemical purity, high specific surface area and narrow distribution of particle size (ranging in tens of nm).Generally, accelerated electrons, gamma, and UV radiation yield materials with comparable properties and structural characteristics, but UV-radiation seems to be the most convenient for preparation of intricate compounds such as synthetic garnets and spinels, while ionizing radiation is better for preparation of compounds doped with foreign ions.Among discussed compounds, only zinc oxide, peroxide and hydroxide were prepared directly via irradiation. For preparation of other crystalline oxidic compounds, mild heat treatment of amorphous or weakly crystalline solid phase was necessary.     

Optical coherence tomography as a method of quality inspection for printed electronics products

Application of time domain, ultra high resolution optical coherence tomography (UHR-OCT) in printed electronics products’ quality inspection is demonstrated. Presented study was done using experimental UHR-OCT device based on a Kerr-lens mode locked Ti:sapphire femtosecond laser, photonic crystal fibre and modified, free-space Michelson interferometer. Possibilities of the technique are demonstrated by analysis of an RF antenna—example of printed electronics products. Measurements were done with submicron axial resolution, offered by UHR-OCT system developed in our laboratory. Such high resolution is necessary due to the thickness of material layers used in printed electronics. In addition to tomography imaging, numerical results were compared with data provided by two commercially available measurement devices: Wyko NT3300 optical profiler and Dektak 8 stylus profiler (both Veeco). Comparison of profile heights and their spatial correlation is presented. Ability for full volumetric reconstruction and accuracy justified with reference measurements prove OCT to be a reliable tool in printed electronics product testing.     

On the electrocatalytical oxygen reduction reaction activity and stability of quaternary RhMo-doped PtNi/C octahedral nanocrystals

Recently proposed bimetallic octahedral Pt–Ni electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC) cathodes suffer from particle instabilities in the form of Ni corrosion and shape degradation. Advanced trimetallic Pt-based electrocatalysts have contributed to their catalytic performance and stability. In this work, we propose and analyse a novel quaternary octahedral (oh-)Pt nanoalloy concept with two distinct metals serving as stabilizing surface dopants. An efficient solvothermal one-pot strategy was developed for the preparation of shape-controlled oh-PtNi catalysts doped with Rh and Mo in its surface. The as-prepared quaternary octahedral PtNi(RhMo) catalysts showed exceptionally high ORR performance accompanied by improved activity and shape integrity after stability tests compared to previously reported bi- and tri-metallic systems. Synthesis, performance characteristics and degradation behaviour are investigated targeting deeper understanding for catalyst system improvement strategies. A number of different operando and on-line analysis techniques were employed to monitor the structural and elemental evolution, including identical location scanning transmission electron microscopy and energy dispersive X-ray analysis (IL-STEM-EDX), operando wide angle X-ray spectroscopy (WAXS), and on-line scanning flow cell inductively coupled plasma mass spectrometry (SFC-ICP-MS). Our studies show that doping PtNi octahedral catalysts with small amounts of Rh and Mo suppresses detrimental Pt diffusion and thus offers an attractive new family of shaped Pt alloy catalysts for deployment in PEMFC cathode layers.

PtNi nano-octahedra with Rh and Mo dopants are highly active catalysts for the oxygen reduction reaction with excellent stability and shape integrity. We investigate the morphological, structural, and compositional evolution during stability testing.